DYNAMICALLY COMPENSATED OPERATIONAL AMPLIFIER

Abstract

An operational amplifier is dynamically compensated depending on the internal state of the operational amplifier. Compensation is fully enabled only when the internal state indicates a risk of instability. When the internal state of the operational amplifier indicates there is no risk of instability, the compensation is totally or partially turned off.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, both as to device and method of operation, together with features and advantages thereof may best be understood by reference to the following detailed description with the accompanying drawings in which:

FIG. 1 depicts a functional block diagram of a dynamically compensated opamp in an embodiment in accordance with the present invention.

FIG. 2 illustrates the two-phase operation of an exemplary switch-capacitor circuit according to the present invention.

FIG. 3 depicts an exemplary output waveform of the switch-capacitor of FIG. 2 during the transfer phase.

FIG. 4A depicts an exemplary embodiment of a dynamically compensated opamp according to the present invention.

FIG. 4B depicts another exemplary embodiment of a dynamically compensated opamp according to the present invention.

FIG. 5 depicts an exemplary compensation controller for the opamp according to the present invention.

FIG. 6 depicts an exemplary state diagram for the finite state machine used for the controller of FIG. 5.

FIG. 7 depicts a schematic diagram of an exemplary comparator circuit suitable for the controller of FIG. 5.

Claims

1. An operation amplifier comprising: a core circuit comprising at least two amplification stages;an adjustable compensation circuit, coupled to at least two nodes of the core circuit, configured to compensate the core circuit; anda compensation controller, coupled to the adjustable compensation circuit, configured to receive at least a voltage signal of a node within the core circuit and generate a control signal to control the adjustable compensation circuit based on the voltage signal.

2. The operational amplifier of claim 1, wherein the adjustable compensation circuit comprises at least a switch.

3. The operational amplifier of claim 2, wherein the control signal comprises at least a buffer circuit coupled to the switch in parallel.

4. The operational amplifier of claim 2, wherein the compensation controller comprises: two comparators for receiving the voltage signal and generating two comparator output signals;a timer circuit for generating a logical signal; anda finite state machine (FSM) for receiving the two comparator output signals and the logical signal and generating the control signal to control the switch of the adjustable compensation circuit.

5. The operational amplifier of claim 4, wherein the two comparators are biased and have a hysteresis.

6. The operational amplifier of claim 4, wherein the FSM comprises at least two states, say a first state and a second state, wherein upon the assertion of the logical signal the FSM enters the first state.

7. The operational amplifier of claim 6, wherein FSM makes the control signal turn off the switch to disable the compensation in the first state and turn on the switch to enable the compensation in the second state.

8. The operational amplifier of claim 6, wherein upon the de-assertion of the logical signal the FSM transits to the second state depending on the two comparator outputs.

9. The operational amplifier of claim 2 being suitable a switch-capacitor circuit.

10. A method of dynamically compensating an operational amplifier comprising a core circuit and a compensation circuit, the method comprising: detecting the internal state of the core circuit based on at least a node voltage within the core circuit to generate a detection signal; andselecting one of first and second compensation modes of the compensation circuit to compensate the core circuit based on the detection signal.

11. The method of claim 10, wherein the internal state of the core circuit is corresponding to a maximum driving capacity of the core circuit.

12. The method of claim 10, wherein the compensation circuit is disabled in the first compensation mode.

13. The method of claim 12, wherein the compensation circuit is disabled when the core circuit is driven at a maximum capacity.

14. The method of claim 10, wherein the compensation circuit is enabled in the first compensation mode.

15. The method of claim 14, wherein the compensation circuit is enabled when the core circuit is driven at a non-maximum capacity.

16. A method of dynamically compensating an operational amplifier comprising a core circuit and a compensation circuit, the method comprising: detecting the internal state of the core circuit based on at least a node voltage within the core circuit; andcontrolling the compensation circuit based on the internal state of the core circuit of the operational amplifier.

17. The method of claim 16, wherein the internal state of the core circuit is corresponding to a maximum driving capacity of the core circuit.

18. The method of claim 17, wherein the compensation circuit is enabled when the core circuit is driven at the non-maximum driving capacity.

19. The method of claim 16, wherein the compensation circuit is disabled when the core circuit is driven at the maximum driving capacity such that the speed of the core circuit is improved.

20. The method of claim 16, wherein the compensation circuit is enabled when the core circuit is driven at the non-maximum driving capacity.